Self-hydrogenated shell promoting photocatalytic H2 evolution on anatase TiO2

Abstract

As one of the most important photocatalysts, TiO 2 has triggered broad interest and intensive studies for decades. Observation of the interfacial reactions between water and TiO 2 at microscopic scale can provide key insight into the mechanisms of photocatalytic processes. Currently, experimental methodologies for characterizing photocatalytic reactions of anatase TiO 2 are mostly confined to water vapor or single molecule chemistry. Here, we investigate the photocatalytic reaction of anatase TiO 2 nanoparticles in water using liquid environmental transmission electron microscopy. A self-hydrogenated shell is observed on the TiO 2 surface before the generation of hydrogen bubbles. First-principles calculations suggest that this shell is formed through subsurface diffusion of photo-reduced water protons generated at the aqueous TiO 2 interface, which promotes photocatalytic hydrogen evolution by reducing the activation barrier for H 2 (H–H bond) formation. Experiments confirm that the self-hydrogenated shell contains reduced titanium ions, and its thickness can increase to several nanometers with increasing UV illuminance.